Summer in the Alpine House

The main flowering season for alpine plants is spring, but there are many mountain plants that flower in summer. You can see plenty of these now in the Davies Alpine House. But why do they flower now?

If you explore high enough altitudes in mountains such as the Alps and Pyrenees in July or August, you will reach elevations where summer has only just arrived. There you can find a range of alpine plants in bloom and meadows filled with colour. The following photograph was taken in the Caucasus Mountains of Georgia, in August, and shows a meadow above the treeline that was full of flowering plants, including Aquilegia, Campanula and the purple Geranium ibericum.

An alpine meadow in the Caucasus Mountains of Georgia

When you grow alpine plants at low altitudes they often flower earlier than they would in their high mountain home, but if you give them enough water and keep them cool, many will keep blooming right into summer. The genus Campanula, the bell-flowers, contains many small, compact mountain plants that flower in summer. Two examples in the Davies Alpine House are Campanula fragilis and C. elatines, both from Italy. Campanula elatines, from the Cottian Alps of north-west Italy, is grown in crumbly tufa rock in the Alpine House because it needs perfect drainage and can easily rot in winter if it gets too wet. This plant flowers right through the summer months.

Left, Campanula fragilis, and right, Campanula elatines

The only true summer-flowering Cyclamen is the European Cyclamen purpurascens. It comes from the Alps and further east into Slovakia and Hungary, and often grows in the dappled shade of woodland, in leafy soil among rocks. This species is found further north than other Cyclamen and is used to cooler summers and colder winters than other species, hence its summer growing season.

Cyclamen purpurascens in the Davies Alpine House

In Turkey, summers are generally hot and dry but growing in limestone crevices in the Taurus Mountains, at altitudes as high as 2,400 m, is Pelargonium endlicherianum. This genus is mainly South African and most species are not hardy, but the habitats of P. endlicherianum can be freezing in winter and this species is hardy enough to survive alpine house conditions, where it too flowers all summer long.

Left, flowers of Pelargonium endlicherianum, and right, two colour forms on display

The Himalayan Mountains, especially the south-facing slopes, are subjected to the summer monsoon, which travels from east to west, dousing the hills and valleys with sometimes huge volumes of water. When the rains arrive the plants get growing, and summer is the flowering season for many Himalayan plants, including lilies, roscoeas and Incarvillea. Planted in the Alpine House is the trailing Incarvillea arguta, with pink flowers on stems a metre or more in length.

Incarvillea arguta, from the Himalaya

If you are lucky you may see the wonderful flowers of Tigridia pavonia in the Davies Alpine House. Each large flower only lasts a day and is best in the morning. This plant species comes from Guatemala and Mexico, where it is dormant in the dry winter months. It grows and flowers in summer when the rains arrive. Like all the plants mentioned here, it is climate that determines flowering time, whether it is the warmth of summer reaching the high Alps, the monsoon advancing along the Himalayan ranges, or the wet season arriving in Central America. It means we can keep the Alpine House looking good all summer long.

Summer flowering Tigridia pavonia

- Richard -

Comments

Peter Taggart

22 September 2011

Comment:

Pelargonium endlicherianum was unscathed, frozen on a bench with me, at -15 to -18C last winter. (I did once kill it through drought in summer though)
I would be glad to try quercetorum.

Really interesting to see the Pelargonium. I have grown this well in the alpine house, where it flowered and set seed very reliably. I was tempted to try it outside on a sand bed but it has not been a success and must require the extra heat and protection under glass. Seedlings showed no variation in flower colour so it is fascinating to see the different forms at Kew. I do grow that other disjunct species, P. quercetorum, in the garden successfully, though it is shy-flowering.